1 files changed, 15 insertions, 17 deletions

diff --git a/lib/Transforms/Utils/BasicBlockUtils.cpp b/lib/Transforms/Utils/BasicBlockUtils.cpp
index 606bd8baccaad..8f59913e14bbf 100644
--- a/lib/Transforms/Utils/BasicBlockUtils.cpp
+++ b/lib/Transforms/Utils/BasicBlockUtils.cpp
@@ -94,9 +94,8 @@ bool llvm::DeleteDeadPHIs(BasicBlock *BB, const TargetLibraryInfo *TLI) {
   // Recursively deleting a PHI may cause multiple PHIs to be deleted
   // or RAUW'd undef, so use an array of WeakTrackingVH for the PHIs to delete.
   SmallVector<WeakTrackingVH, 8> PHIs;
-  for (BasicBlock::iterator I = BB->begin();
-       PHINode *PN = dyn_cast<PHINode>(I); ++I)
-    PHIs.push_back(PN);
+  for (PHINode &PN : BB->phis())
+    PHIs.push_back(&PN);
 
   bool Changed = false;
   for (unsigned i = 0, e = PHIs.size(); i != e; ++i)
@@ -134,24 +133,17 @@ bool llvm::MergeBlockIntoPredecessor(BasicBlock *BB, DominatorTree *DT,
   if (!OnlySucc) return false;
 
   // Can't merge if there is PHI loop.
-  for (BasicBlock::iterator BI = BB->begin(), BE = BB->end(); BI != BE; ++BI) {
-    if (PHINode *PN = dyn_cast<PHINode>(BI)) {
-      for (Value *IncValue : PN->incoming_values())
-        if (IncValue == PN)
-          return false;
-    } else
-      break;
-  }
+  for (PHINode &PN : BB->phis())
+    for (Value *IncValue : PN.incoming_values())
+      if (IncValue == &PN)
+        return false;
 
   // Begin by getting rid of unneeded PHIs.
   SmallVector<Value *, 4> IncomingValues;
   if (isa<PHINode>(BB->front())) {
-    for (auto &I : *BB)
-      if (PHINode *PN = dyn_cast<PHINode>(&I)) {
-        if (PN->getIncomingValue(0) != PN)
-          IncomingValues.push_back(PN->getIncomingValue(0));
-      } else
-        break;
+    for (PHINode &PN : BB->phis())
+      if (PN.getIncomingValue(0) != &PN)
+        IncomingValues.push_back(PN.getIncomingValue(0));
     FoldSingleEntryPHINodes(BB, MemDep);
   }
 
@@ -331,6 +323,12 @@ static void UpdateAnalysisInformation(BasicBlock *OldBB, BasicBlock *NewBB,
   bool IsLoopEntry = !!L;
   bool SplitMakesNewLoopHeader = false;
   for (BasicBlock *Pred : Preds) {
+    // Preds that are not reachable from entry should not be used to identify if
+    // OldBB is a loop entry or if SplitMakesNewLoopHeader. Unreachable blocks
+    // are not within any loops, so we incorrectly mark SplitMakesNewLoopHeader
+    // as true and make the NewBB the header of some loop. This breaks LI.
+    if (!DT->isReachableFromEntry(Pred))
+      continue;
     // If we need to preserve LCSSA, determine if any of the preds is a loop
     // exit.
     if (PreserveLCSSA)